A large number of methods for amplifying a nucleic acid have been reported so far. Examples of such a method for amplifying a nucleic acid include Polymerase Chain Reaction (PCR) (Non Patent Literature 1), Strand Displacement Amplification (SDA) (Non Patent Literature 2), Multiple Displacement Amplification (MDA) (Non Patent Literature 3), Rolling-Circle Amplification (RCA) (Non Patent Literature 4), Loop-Mediated Isothermal Amplification (LAMP) (Non Patent Literature 5), Smart Amplification Process (SmartAmp) (Non Patent Literature 6), Helicase-Dependent Amplification (HDA) (Non Patent Literature 7), and Ligase Chain Reaction (LCR) (Non Patent Literature 8). These methods are amplification methods of using DNA as a template, and in all of the methods other than PCR, HDA and LCR, the strand displacement activity of DNA polymerase is utilized. A main amplification system of utilizing a strand displacement reaction is SDA (Non Patent Literature 2). In SDA, a cleavage site (nick) is made on one strand of double-stranded DNA using a restriction enzyme or the like. Using this nick as a starting point, the DNA strand on the 3′ side is peeled by the strand displacement activity of DNA polymerase, and novel complementary DNA is synthesized. SDA is a technique of amplifying complementary DNA by continuously generating this reaction. Moreover, MDA, which utilizes a random hexamer primer, is able to randomly take place a strand displacement reaction by randomly annealing primers to multiple sites on template DNA, and thus, this is a method having an extremely high amplification rate (Non Patent Literature 3). However, in order to amplify an RNA sequence according to these amplification methods using DNA as a template, it is necessary to perform a reverse transcription reaction of converting RNA to DNA. In addition, in the case of SDA, since a nick needs to be inserted into template DNA using restriction enzymes, it is necessary to add a restriction enzyme recognition sequence, deoxyinosine and the like to the template. Moreover, in the case of LAMP and SmartAmp, four or five sequence-specific primers are necessary for a single target. Thus, the synthesis of a special oligo primer, the designing of a sequence-specific primer, and the like become necessary. Furthermore, amplification methods using DNA as a template, such as PCR as a representative example, are problematic in terms of pseudo-positive results generated as a result of the carry-over of the previous PCR amplification products or reverse transcription products on samples, and non-specific products derived from DNA contaminated with reagents, DNA mixed from working environment, etc. (Non Patent Literatures 9 and 10). In particular, in the case of MDA, since primers are randomly annealed to DNA, it is likely that such contaminated DNA-derived non-specific products would be increased. As an amplification technique of using RNA as a template, a method of utilizing a special DNA hairpin primer having a restriction enzyme recognition sequence has been proposed. In this method, a cleavage point is generated on a DNA hairpin primer that has been allowed to bind to RNA as a template, and then, a strand displacement reaction is allowed to take place, so as to amplify complementary strand DNA. In this method, however, a pre-treatment needs to be performed to ligate a DNA hairpin primer to the 3′-end of template RNA, and thus, molecules that cannot be captured are likely to be generated depending on ligation conditions. Further, since amplification is started from the 3′-end of template RNA, it is considered difficult for this method to equally amplify the entire-length DNA.